The present invention relates generally to a double annular combustor for a gas turbine engine and, in particular, to a fabricated cowl for such double annular combustor having stiffening ribs which are welded into position.
In a gas turbine engine, pressurized air is provided from the compressor stage to the combustor, whereupon it is mixed with fuel and is burned in the combustion chamber. The amount of pressurized air which enters the fuel/air mixers, and correspondingly the inner an outer passages of the combustor, has typically been regulated by inner and outer cowls located upstream of the fuel/air mixers and the combustor dome.
In the case of double annular combustors, the inner and outer annular portions of the cowl are separated by a greater distance, but generally include a middle annular portion positioned therebetween. Windows are typically provided in the inner and outer annular cowl portions to enable fuel nozzles to interface with the fuel/air mixers, as well as permit cooling air to flow along the forward sides thereof. Because of the radial height required for cowls of double annular combustors, such cowls are subjected to changes in pressure loads and inner and outer compressive loads induced by thermal growth of the inner and outer liners connected thereto.
Accordingly, the prior cowl design utilized in double annular combustors has been cast and incorporates a plurality of radial members or ribs extending from the forward and aft side to assist in providing stiffness to the cowl structure. It will be appreciated that such ribs, which provide structural integrity thereto, are machined to a desired thickness. It has been found, however, that temperature gradients exist between the forward surface of the cowl and the ribs located on the aft side thereof. Such thermal mismatch then induces stresses at the interface of the rib and annulus which can impact low cycle fatigue life.
In light of the foregoing, it would be desirable for a cowl to be developed for multiple annular combustors which not only achieves the necessary structural requirements, but also minimizes any thermal gradients with the ribs therein. It would also be desirable for such a cowl to be lighter and less costly while maintaining the same air flow characteristics so as to avoid recertification of the combustor.